#include<bits/stdc++.h>
using namespace std;
double account(double x1, double y1, double x2, double y2)
{
	double res = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
	return res;
}
int main()
{
	double a, b, c, d;
	while (cin >> a >> b >> c >> d) {
		cout << fixed << setprecision(2) << account(a, b, c, d);
	}
	return 0;
}
